Method of manufacturing a semiconductor device from which damage layers and native oxide films in connection holes have been removed

ABSTRACT

An insulating film formed on a conducting layer is dry-etched so as to make a connection hole in the insulating film to expose the conducting layer. Plasma is supplied onto the exposed conducting layer to dry-clean a damage layer produced in the connection hole. A product produced in the connection hole as a result of the dry cleaning is removed by a wet process. An oxide film formed in the connection hole as a result of the wet process is etched by a chemical dry process using a gas including either NF 3  or HF. A thermally decomposable reaction product produced as a result of the etching is removed by heat treatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-029454, filed Feb. 4, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device manufacturing method,and more particularly to a method of making connection holes, such ascontact holes.

2. Description of the Related Art

In a semiconductor device, plugs made of conducting material have beenused. Each of the plugs electrically connects a transistor to a wiringlayer above the transistor or a lower wiring layer to an upper wiringlayer. To do this, a connection hole, such as a contact hole or a viahole, is made in the insulating film covering the transistor or in theinsulating film between the lower wiring layer and upper wiring layerand then is filled with conducting material, thereby forming a plug.

For instance, when a contact hole is made, an insulating film is etchedusing, for example, RIE (Reactive Ion Etching) techniques. In thisetching, a damage layer is formed on the sidewall and at the bottom ofthe contact hole. The damage layer is removed by, for example, a wetprocess. However, the surface of the conducting layer, such as a metalsilicide layer, exposed at the bottom of the contact hole after thedamage layer has been removed is non-uniform. Moreover, during theremoval of the damage layer, another damage layer and a native oxidefilm are formed. When a barrier metal is formed in the contact hole withthe damage layer and native oxide film being left as described above,the contact resistance increases and the characteristic of thetransistor deteriorates. Therefore, it is necessary to remove the damagelayer and native oxide film completely.

To remove a damage layer formed in a contact hole, techniques using onlydry cleaning have been developed (refer to, for example, Jpn. Pat.Appln. KOKAI Publication No. 2000-236021).

In the conventional cleaning method, however, it was difficult tosufficiently remove the damage layer and native oxide film in thecontact hole. Therefore, a semiconductor device manufacturing methodcapable of sufficiently removing the damage layer and native oxide filmin the contact hole has been desired. Furthermore, when a contact holeis made in a plurality of insulating films stacked one on top ofanother, steps might develop in the contact hole. Therefore, thedevelopment of the technique for removing the steps has been desired.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided asemiconductor device manufacturing method comprising: dry-etching aninsulating film formed on a conducting layer so as to make a connectionhole in the insulating film to expose the conducting layer; supplyingplasma excited from an oxidized gas onto the exposed conducting layer todry-clean a damage layer produced in the connection hole; removing aproduct produced in the connection hole as a result of the dry cleaningby a wet process; etching an oxide film formed in the connection hole asa result of the wet process by a chemical dry process using a gasincluding either NF₃ or HF; and removing a thermally decomposablereaction product as a result of the etching by heat treatment.

According to a second aspect of the invention, there is provided asemiconductor device manufacturing method comprising: dry-etching asilicon nitride film and a silicon oxide film stacked on a conductinglayer so as to make a connection hole in the silicon nitride film andsilicon oxide film to expose the conducting layer; etching steps in thesilicon nitride film and silicon oxide film formed in the connectionhole by chemical dry process using a gas including either HF₃ or HF; andremoving a thermally decomposable reaction product as a result of theetching by heat treatment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1A to 1E are sectional views to explain a semiconductor devicemanufacturing method according to a first embodiment of the presentinvention;

FIG. 2 shows the result of analyzing a semiconductor device processed bythe method of the first embodiment and a conventional manufacturingmethod by use of X-ray photoelectron spectroscopy;

FIG. 3 shows the result of analyzing a semiconductor device processed bythe method of the first embodiment and the conventional manufacturingmethod by use of X-ray photoelectron spectroscopy;

FIGS. 4A and 4B relate to the first embodiment, showing transmissionelectron microscope (TEM) photographs illustrating the states of thesemiconductor device before and after a wet process;

FIG. 5 shows variations in the contact resistance caused by a dryprocess and a wet process;

FIG. 6 shows the result of analyzing a semiconductor device processed bythe method of the first embodiment by use of X-ray photoelectronspectroscopy;

FIG. 7 shows variations in the contact resistance of the firstembodiment and in a conventional contact resistance; and

FIGS. 8A, 8B, and 8C are sectional views to help explain a semiconductordevice manufacturing method according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, referring to the accompanying drawings, embodiments of thepresent invention will be explained.

First Embodiment

FIGS. 1A to 1E are sectional views to explain a semiconductor devicemanufacturing method according to a first embodiment of the presentinvention. The first embodiment shows an example of forming a metalcontact with, for example, a silicide layer.

As shown in FIG. 1A, a silicide layer 12 acting as a conducting layer isformed at the surface of, for example, a silicon substrate 11. Thesilicide layer 12 is any one of, for example, CoSix, NiSix, ErSix,PtSix, and Pd₂Six. However, the silicide layer 12 is not limited tothese. In this embodiment, the silicide layer 12 is made of NiSi. Thus,hereinafter, the silicide layer 12 is referred to as the NiSi layer 12.On the NiSi layer 12, an insulating layer, such as a silicon oxide film13, is formed. The insulating film is not limited to a silicon oxidefilm. Another material may be used as the insulating film.

Next, as shown in FIG. 1B, the silicon oxide film 13 is etched by RIEtechniques, with, for example, a resist pattern (not shown) as a mask,thereby making a connection hole, such as a contact hole 14. Forexample, H₂-added CF₄ gas is used as the etching gas. At the bottom ofthe contact hole 14 formed as described above, a damage layer 15 isformed. The damage layer 15, which includes damage and etching productsproduced as a result of the etching, is made chiefly of, for example, F,C, and Si—O as shown in (1) of FIG. 2. FIG. 2 lists the proportions ofelements observed in analyzing a semiconductor device processed by themethod of the first embodiment and a conventional manufacturing methodby use of XPS (X-ray photoelectron spectroscopy).

As described above, after the etching, the damage layer 15 exists at thebottom of the contact hole 14. The result of analysis by XPS has shownthat the NiSi combined peak exposed at the bottom of the contact hole 14is small as shown in (1) of FIG. 3.

In the prior art, after a contact hole was made, cleaning was done in awet process. The wet process was carried out to remove F and C producedin making the contact hole and the oxide film formed at the bottom ofthe contact hole. The results of analysis made by XPS after the wetprocess are shown in (2) of FIG. 2 and (2) of FIG. 3. By such a wetprocess, F and C are removed as shown in (2) of FIG. 2. However, asshown in FIG. 4B, an oxide film of about 5 nm in thickness is newlyformed at the surface of NiSi at the bottom of the contact hole.Therefore, it is difficult to sufficiently clean the surface of the NiSilayer only by the wet process. As shown by (1) of FIG. 6, the result ofanalysis by XPS has shown that the peak of Ni—Si is small due to theoxide film formed on the surface of the NiSi layer. Furthermore, asshown by (1) of FIG. 5, the formed oxide film has contributed to anincrease in the contact resistance in the wet process.

To overcome this problem, it is conceivable that instead of the wetprocess, a dry process using NF₃ gas is carried out as disclosed in Jpn.Pat. Appln. KOKAI Publication No. 2000-236021. In the dry process, anoxide film is not formed on the NiSi layer after F and C are removed.However, the dry process lacks the capability of removing the etchingdamage layer caused in making a contact hole. Therefore, as shown in (2)of FIG. 5, simply replacing the wet process with the dry process resultsin an increase in the contact resistance as compared with the wetprocess shown in (1) of FIG. 5.

In the first embodiment, to overcome this drawback, for example, afterthe resist pattern is removed, an ashing process is carried out for drycleaning to remove the etching damage layer 15 formed in making thecontact hole. In the ashing process, plasma excited from oxidized gas,such as oxygen gas (O₂) or ozone (O₃), is used. Moreover, it isdesirable that the temperature of the substrate 11 in the ashing processshould be in the range from, for example, 150° C. or higher to 400° C.or lower. If the temperature is lower than 150° C., it is difficult toremove the damage layer 15 sufficiently. In addition, when the NiSilayer 12 is formed into, for example, the source and drain region or thegate electrode of a transistor, it is difficult to process thetransistor at a temperature higher than 400° C. without thedeterioration of the characteristic of the transistor. To obtain abetter result, it is desirable that the temperature of the substrate 11should be in the range from 250° C. or higher to 300° C. or lower. Asdescribed above, subjecting the damage layer 15 to the ashing processmakes it possible to remove F and C constituting the damage layer 15almost completely as shown in (3) of FIG. 2.

However, when the ashing process is carried out, an ashing product 16 isformed at the surface of the NiSi layer 12 as shown in FIG. 1C. Theproduct 16 includes, for example, Si—O and Ni—O (F) as shown by (2) ofFIG. 6 and in (3) of FIG. 3. Moreover, the peak value of Ni₂O₃ producedin the ashing process shown by (2) of FIG. 6 is so large that Ni—O (F)is difficult to remove by a dry process.

In the first embodiment, to overcome this problem, the product 16produced in the ashing process (hereinafter, referred to as the Ni—O (F)layer 16) is removed by a wet process. In the wet process, the productis treated with, for example, sulfuric acid-hydrogen peroxide mixturemade of sulfuric acid and hydrogen peroxide solution. Thereafter, thetreated product is further treated with hydrogen peroxide solution andcholine solution. As described above, carrying out the wet process afterthe ashing process enables the Ni—O (F) layer 16 to be removed.

Each of (3) of FIG. 6, (4) of FIG. 2, and (4) of FIG. 3 shows a casewhere a wet process is carried out after an ashing process. As seen from(3) of FIG. 6, the peak value of NiSi appearing at the bottom of thecontact hole 14 is larger than when only a wet process is carried out asshown by (1) of FIG. 6. That is, it is seen that the damage layer 15 andNi—O (F) layer 16 have been removed sufficiently by the ashing processand wet process.

However, when the wet process is carried out, a native oxide film 17 isformed at the bottom of the contact hole 14 as shown in FIG. 1D. Thus,the native oxide film 17 at the bottom of the contact hole is removed bysoft-etching the native oxide film by a chemical dry process using a gasincluding, for example, either HF₃ or HF. It is desirable that the gasshould be a combination of, for example, NF₃ and NH₃, of NF₃, N₂, andH₂, or of HF and NH₃. In addition, it is desirable that the temperatureof the substrate 11 in the chemical dry process should be in the rangefrom, for example, −20° C. or higher to +30° C. or lower. If theprocessing temperature is lower than −20° C. or higher than +30° C., itis difficult to etch the native oxide film. To obtain much betterresults, it is desirable that the processing temperature should be inthe range from −20° C. or higher to +25° C. or lower.

Thereafter, a small amount of thermally decomposable reaction product,such as (NH₄)₂SiF₆, (not shown) produced in etching to remove the nativeoxide film is removed by heat treatment. It is desirable that thetemperature of the substrate 11 in the heat treatment should be in therange of, for example, 100° C. or higher to 400° C. or lower. If thetemperature is lower than 100° C., it is difficult to remove the productsufficiently. If the temperature is higher than 400° C., the performanceof the transistor can deteriorate. To obtain much better results, it isdesirable that the temperature of substrate 11 should be in the rangefrom 150° C. or higher to 400° C. or lower. However, the upper limittemperature can be raised in the range allowed by the performance of thetransistor. Furthermore, it is desirable that the chemical dry processand heat treatment should be carried out without the rupture of vacuumto prevent the re-formation of a native oxide film. That is, it isdesirable that these processes should be carried out consecutively in avacuum.

The native oxide film 17 at the bottom of the contact hole can beremoved by the chemical dry process and heat treatment, which enablesthe surface of the NiSi layer 12 to be exposed as shown in FIG. 1E. Asdescribed above, after the contact hole 14 is made, the ashing process,wet process, chemical dry process, and heat treatment are carried outsequentially, thereby removing the etching damage layer 15, Ni—O (F)layer 16, and native oxide film 17 from the surface of the NiSi layer12, which causes the clean NiSi layer 12 to be exposed as shown by (4)of FIG. 6, in (5) of FIG. 2, and in (5) of FIG. 3.

Thereafter, inside the contact hole 14, a single-layer or multilayerbarrier metal 18 is made of metal material by, for example, sputteringor CVD techniques. Then, the contact hole 14 is filled with metalmaterial (not shown), thereby forming a contact plug. As the metalmaterial, for example, Ti, TiN, Ta, TaN, W, WN, Cu, Al, or the like isused.

As described above, a film of a barrier metal 18 is formed at thesurface of the clean NiSi layer 12, thereby realizing a stabler, lowercontact resistance as shown by (1) of FIG. 7 than that of a conventionalequivalent shown by (2) of FIG. 7.

It is desirable that the barrier metal should be formed in consecutiveprocesses without the exposure of the NiSi layer 12 at the bottom of thecontact hole to the air. Therefore, a barrier metal is formed, forexample, in another chamber connected and clustered with the chamberused to make the contact hole.

In the first embodiment, the contact hole 14 is made in the siliconoxide film 13 on the NiSi layer 12. After the resist is removed, theashing process as dry cleaning, wet process, chemical dry process, andheat treatment are carried out in sequence, thereby removing the etchingdamage layer 15, Ni—O (F) layer 16, and native oxide film 17 from thesurface of the NiSi layer 12. Therefore, the clean NiSi layer 12 can beexposed at the bottom of the contact hole 14, which enables a stable,low contact resistance to be realized.

Second Embodiment

In the first embodiment, the damage layer, etching product, and nativeoxide film in a contact hole have been removed. The processes in thefirst embodiment can be applied to alleviate the steps in a contact holemade in a plurality of insulating films differing in, for example, theetching selection ratio.

Specifically, to reduce the heat history in the post-process of the NiSior shallow diffused layer, a silicon nitride film and a silicon oxidefilm formed by, for example, CVD techniques are applied to the contactprocess. The etching speeds of these silicon nitride film and siliconoxide film in dry etching and wet etching are faster than that of anoxide film formed at 800° C. or higher in the prior art. The differencein etching speed is particularly large in wet etching. Specifically, theetching speed of a silicon nitride film with a fluoric acid (HF)solution is, for example, 10 or more times as fast as that of an oxidefilm formed at 800° C. or higher. Moreover, the etching speed of asilicon oxide film with a fluoric acid solution is, for example, two ormore times as fast as that of an oxide film formed at 800° C. or higher.Therefore, when a contact hole is made in a stacked layer of a siliconnitride film and a silicon oxide film by RIE techniques, or when a wetprocess is carried out in a pretreatment in forming a barrier metal in acontact hole, steps develop at the sidewall of the contact hole. In thisstate, when a barrier metal is formed in the contact hole, the coverageof the contact hole with the barrier metal deteriorates. Consequently,there is possibility that an increase in the contact resistance and aleak may occur.

To overcome this problem, a second embodiment of the present inventionalleviates the steps in the contact hole by applying the processes ofthe first embodiment.

Hereinafter, a semiconductor device manufacturing method according tothe second embodiment will be explained.

FIGS. 8A, 8B, and 8C show a semiconductor device manufacturing methodaccording to the second embodiment.

As shown in FIG. 8A, a silicon nitride film 22 is formed at the surfaceof, for example, a conducting layer 21 by, for example, a CVD method. Onthe silicon nitride film 22, a silicon oxide film 23 is formed by, forexample, a CVD method. The conducting layer 21 is, for example, silicon,polysilicon, amorphous silicon, CoSi₂, NiSi, TiN, W, or WN and is notlimited to these.

Next, as shown in FIG. 8B, with a resist pattern (not shown) as a mask,the silicon oxide film 23 and silicon nitride film 22 are etched by RIEtechniques, thereby making a contact hole 24 in the silicon oxide film23 and silicon nitride film 22. As the etching gas, for example, a gasobtained by adding H₂ to CF₄ or a gas of the NF₃ family is used. As aresult of the etching, steps or damage layers are produced in thecontact hole 24.

Thereafter, as in the first embodiment, the damage layer (not shown) isremoved by dry cleaning, such as an ashing process. Then, the resultinglayer is subjected to a wet process with, for example, sulfuricacid-hydrogen peroxide mixture, hydrogen peroxide solution, and cholinesolution in sequence. By the wet process, the product produced in theashing process is removed. In the wet process, steps 25 are formed dueto the difference in etching speed between the silicon nitride film 22and the silicon oxide film 23 as shown in FIG. 8B. The steps 25 are, forexample, about 1 nm in height.

Thereafter, a chemical dry process is carried out using a gas includingeither NF₃ or HF. By this dry etching, the inner wall of the siliconoxide film 23 in the contact hole 24 is etched, thereby alleviating thesteps 25 formed at the sidewall of the contact hole 24 as shown in FIG.8C.

Then, as in the first embodiment, the thermally decomposable reactionproduct produced in the chemical dry process is removed by heattreatment.

Thereafter, a barrier metal 26 composed of a single layer or a pluralityof layers is formed by, for example, sputtering or CVD techniques. Then,for example, a metal layer 27 is formed in the contact hole 24.

In the second embodiment, after the contact hole 24 is formed, an ashingprocess as dry cleaning, a wet process, a chemical dry process with agas including either NF₃ or HF, and heat treatment are carried out. As aresult, the steps 25 formed in the contact hole 24 are alleviated.Accordingly, when barrier metal is formed in the contact hole 24, thecoverage inside the contact hole is good, which prevents the contactresistance from increasing and a leak from occurring.

In the second embodiment, to remove the steps in the contact hole, allof the ashing process, wet process, chemical dry process with a gasincluding either NF₃ or HF, and heat treatment need not be carried out.At least a chemical dry process with a gas including either NF₃ or HFand heat treatment has only to be carried out.

Furthermore, in each of the first and second embodiments, the case wherea contact hole is made has been explained. This invention is not limitedto this. For instance, the first and second embodiments may be appliedto the formation of a via hole connecting a lower-layer wiring line toan upper-layer wiring line.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1.-10. (canceled)
 11. A semiconductor device manufacturing methodcomprising: dry-etching a silicon nitride film and a silicon oxide filmstacked on a conducting layer so as to make a connection hole in thesilicon nitride film and silicon oxide film to expose the conductinglayer; etching steps in the silicon nitride film and silicon oxide filmformed in the connection hole by a chemical dry process using a gasincluding either NF₃ or HF; and removing a thermally decomposablereaction product produced as a result of the etching by heat treatment.12. The semiconductor device manufacturing method according to claim 11,further comprising: supplying plasma excited from oxidized gas onto theexposed conducting layer after the formation of the connection hole todry-clean a damage layer produced in the connection hole; and removing aproduct produced in the connection hole as a result of the dry cleaningby a wet process before the chemical dry process.
 13. The semiconductordevice manufacturing method according to claim 12, wherein the wetprocess uses a solution including hydrogen peroxide.
 14. Thesemiconductor device manufacturing method according to claim 12, whereinthe oxidized gas includes one of oxygen gas and ozone.
 15. Thesemiconductor device manufacturing method according to claim 12, whereinthe dry cleaning is performed at a temperature in the range from 150° C.or higher to 400° C. or lower.
 16. The semiconductor devicemanufacturing method according to claim 11, wherein the chemical dryprocess and heat treatment are executed consecutively in a vacuum. 17.The semiconductor device manufacturing method according to claim 16,wherein the chemical dry process is carried out at a temperature in therange from −20° C. or higher to +30° C. or lower.
 18. The semiconductordevice manufacturing method according to claim 16, wherein the heattreatment is carried out at a temperature in the range from 100° C. orhigher to 400° C. or lower.
 19. The semiconductor device manufacturingmethod according to claim 11, wherein the conducting layer is one ofsilicon, polysilicon, amorphous silicon, CoSi₂, NiSi, TiN, W, and WN.20. The semiconductor device manufacturing method according to claim 11,further comprising: forming a conducting barrier layer at the innersurface of the connection hole after the heat treatment; and forming acontact plug inside the connection hole.